1. Technical Field
The invention relates to automotive occupancy sensor (AOS) systems for sensing the occupancy state of a vehicle including the location and/or nature of the occupant with respect to the vehicle interior, and more particularly to a linear or spaced array of ultrasound (US) transducers, used alone or with other sensors, mounted adjacent or in the headliner of a vehicle as part of an AOS system. In the preferred embodiment array permits the occupancy state of one or more seats in the vehicle to be determined by a AOS classification algorithm using only US echo range data, thereby reducing the cost and complexity of the system, improving speed and simplifying calibration.
2. Background Art
Studies have revealed that there is a class of automotive accidents causing injuries associated with airbag deployment and with the nature and position of the vehicle occupant, particularly with respect to airbags deployed toward seats occupied by children or infants in car seats. Automotive occupancy sensor (AOS) systems used in conjunction with cooperating airbag deployment systems (ADS) have been developed to regulate the deployment of the airbag. AOS occupancy determination is used by the ADS to cause airbag deployment to be aborted, deferred, modified as to rate, timing or amount of inflation, selecting which of several airbags to deploy, or otherwise to regulate airbag deployment in response to the occupancy state of the adjacent vehicle interior as classified or determined by the AOS. These are also known as xe2x80x9cSmart Airbag Systemsxe2x80x9d. Originally proposed for front airbag systems, smart airbag systems may likewise include AOS for deployment regulation of side airbag systems. For background on AOS systems see Corrado, et al., U.S. Pat. No. 5,482,314 issued Jan. 9, 1996, and also Corrado, et al., U.S. Pat. No. 5,890,085, issued Mar. 30, 1999, and references cited therein, which patents are hereby incorporated by reference.
AOS systems may utilize various types of sensors which produce signals which provide information relating to occupancy state. These include pressure sensors, contact sensors, infra-red sensors, capacitance sensors, visible light sensors and the like. Ultrasound (US) transducers also may be included in AOS systems as active sensors; echoes of US signals transmitted by the transducer are detected by the transducer when reflected back from the vehicle interior and occupants.
AOS systems typically employ sensor systems and relatively complex classification and probability-based decision algorithms which require analysis of a number of different shape, timing and amplitude related aspects of the reflected US signals, in addition to the range of the principal US echo source. In some systems such analysis requires relatively expensive, high-sensitivity US transducers and relatively complex algorithms which process data gathered over relatively large time intervals to classify the occupancy state of the vehicle interior, increasing the amount of time required to arrive at a reliable classification determination. Environmental factors can induce distortions and noise in the US signal, complicating the task of reliable occupancy classification and/or state determination. In addition, the task of constructing a comparative database and designing the microprocessors and associated circuitry to handle the complex algorithm logic is reflected in the overall system development cost and per unit price.
There is a need for an inexpensive, reliable AOS system which can be widely and promptly implemented in production automobiles, especially in light of currently proposed advanced airbag control requirements, such as NHTSA 98-4405, Notice 1 RIN 2127-AG70. There is a need for an AOS sensor system which is inexpensive, reliable, robust (including against environmental disturbances) and which permits simplified, rapid classification based on quantitative US echo range data.
It is a principal object and advantage of the invention to provide an array of ultrasound (US) transducers mounted adjacent or in the headliner of the passenger compartment of a vehicle which can provide signals for AOS occupancy classification and/or state determination based principally on simple echo range data. It is another object and advantage of the invention to provide an inexpensive durable sensor system which is easy to install, calibrate and maintain, and which is robust to environmental disturbances. It is another object and advantage of the invention to provide a sensor system which permits simplified and accelerated signal and classification, and/or state determination processing. Other objects and advantages will be evident from the descriptions, drawings and claims of this invention.
The linear AOS transducer array consists of a plurality of transducers, typically 2 to 8, preferably from about 4 to 6 per seat, in a spaced array, preferably mounted within the headliner adjacent the vehicle roof. In principal embodiments the array is an ordered array, generally spanning front to back in the passenger compartment. One preferred embodiment of the array comprises a linear strip of transducers generally parallel to the vehicle centerline mounted recessed into the headliner either generally above or to one side of the aft centerline normal seat position. The array is preferably located slightly to the outboard side of the normal head position, i.e. the fore/aft centerline of the seat. For a front seat occupant, such as the front seat passenger, the array preferably extends from near the rear edge of the sunvisor in front of the seat to about the longitudinal position of the seat headrest when the seat is adjusted to its most rearward position.
Unless the context implies a more restricted meaning, the term xe2x80x9coccupantxe2x80x9d and the term xe2x80x9cobjectxe2x80x9d are used herein to refer to a person(s) or object(s) occupying the seat and/or the volume above a seat (e.g., a driver, passenger, child or infant seat, passenger sitting on another passenger""s lap, as parcels, animals or objects resting on a seat, and the like) the presence, motion and/or position of which are relevant to the safety criteria used to determine whether a particular airbag system in a vehicle should be deployed, enabled, disabled, aborted or deployed in a modified manner.
There may be a second AOS array symmetrically mounted on the opposite side of the vehicle centerline to provide occupancy determination for the driver and/or other front seat occupants. Arrays may be provided for occupant seats behind the driver/front passengers, i.e. in the middle or rear seating areas as desired. While the arrays are described herein in the present best mode as linear and generally parallel to the centerline, they also may be transverse or diagonal, as in a patterned array, e.g. at the vertices of a triangle, diamond or other polygon.
The transducers of the array are directed generally downward to transmit a generally parallel spaced set of US pulses. The downwardly directed set of pulses cover (xe2x80x9cbathexe2x80x9d or xe2x80x9cpaintxe2x80x9d) a volume of the vehicle interior denoted as the head zone (generally referred to herein as xe2x80x9cH-zonexe2x80x9d), which is a pre-selected occupancy zone. The H-zone is preferably defined by the volume in which the head and/or shoulders of an occupant will be present under circumstances under which the AOS classification algorithm determines that the airbag is to be enabled for deployment, or conversely, is to be aborted or disabled. The specific bounds of the H-zone are ordinarily preselected, based, e.g., on airbag characteristics for deployment safety and injury criteria. Likewise, if there is no occupant, or the occupant is out-of-position with respect to the H-zone so that the head and/or shoulders of the occupant do not intrude into the H-zone, the AOS classification algorithm determines that the airbag is to be disabled or not enabled, as the case may be, enabled with modified inflation rate, level or timing; or otherwise modified for deployment or nondeployment. An example of an out-of-position state (OOPS) is a seated child whose head is below the H-zone boundary, or an adult passenger leaning forward towards the dashboard or reclining backward, with head below and/or forward or back of the H-zone boundary.
The AOS electronic circuitry maybe conventional. The US pulse is reflected from the surfaces lying below the transducer and the reflected echo is received by each respective transducer to produce an input signal to the AOS electronics. Range data is determined from the input signal by the AOS electronics to determine the distance of the object or surface producing the primary echo, such as an occupant""s head or body, an infant seat, a seat cushion, parcels resting on the seat, etc. Collectively, the range data for the transducer array permits the AOS classification algorithm to determine if an object, such as the head, is within the H-zone, and to determine the object""s fore-to-aft position within the H-zone.
Optionally the time history of the range data for each transducer can be used to determine whether an occupant (i.e., occupant""s head and/or shoulders) is moving with respect to the vehicle and seat, such as when a passenger is moving or leaning forward, and this may used as an input in determining whether the airbag deployment is to be enabled, disabled or modified.
Because the AOS transducer array of the invention permits occupancy classification based on US range information, transducers of lower sensitivity may be used, as compared to systems which require more complex qualitative and amplitude sensitive information to be extracted from the input signal. Thus, inexpensive, lower sensitivity lead zirconate/titanate (PZT) type transducers may be employed, offering a number of important advantages over the higher sensitivity transducers conventionally required for AOS systems. PZT sensors are robust, inexpensive, do not require protective grills, may be produced as very thin disks, and can be flush-mounted in the headliner with no projections. Because the PZT sensors are generally directed perpendicularly downward in the arrays of the invention, they may be, if desired, be comparatively larger without projecting from the headliner surface, the larger size compensating for and permitting reduced sensitivity.
All the sensors, electronics, and detection logic are preferably housed inside a single, self-contained unit. The transducers are typically mounted on a thin, elongated mounting board, which optionally also integrally mounts the AOS electronic circuitry, processors, interconnecting leads and an exterior trim surface or cover. Due to the thin profile of the PZT transducers (about 2 to 5 mm thick), an integral transducer array/AOS unit may be mounted entirely between the roof and the headliner, an area typically with a depth on the order of 20xc2x1 mm, and generally unused for other functions. For the preferred PZT sensors, no grill is needed, and the sensor surface, as well as the surface of the array unit, can be painted in any desired color that matches the interior so as to xe2x80x9cblend inxe2x80x9d with the headliner. Optionally a decoratively textured coating may be applied to the trim or/and the transducers.
The length of the H-zone and the transducer array may be selected to take into account the range of occupant head position based on the range of seat fore/aft adjustment. The H-zone extent may be defined differently for a driver seat and a passenger seat, taking into account, among other things, the typically different positions of the airbag installation. The spacing and number of the transducers of the array may be selected to provide adequate discrimination between the occupant""s head and other fixed objects, such as a seat headrest. Preferably, the spacing and number of transducers is selected so that the headrest, if present, will give a US echo range return on at least one transducer. Also the transducers spacing and number is preferably selected so that the occupant""s head will give a range return on more than one transducer, more preferably at least three.
The position of the occupant within H-zone is determined by an AOS algorithm based on the H-zone definition (configuration and location in the compartment) and the pattern of range returns from the transducers of the array. Typically, the algorithm is implemented by code written in conventional computer or device languages, or is implemented by logic circuitry comprising conventional devices. The method and algorithm of determining occupant position of the present invention as described herein can be executed by the AOS electronics which includes suitable hardware and/or software and/or firmware running on a suitable processor. Typically, the firmware or software is accessed by a processor using any suitable reading device which can read the medium on which the software or firmware is stored, such as any suitable processor-readable storage medium. The storage medium includes, for example, magnetic storage media, or solid state electronic storage devices such as random access memory (RAM) or read only memory (ROM); or any other physical device or medium employed to store a computer program. The software or firmware carries program code which, when read by the processor, causes the computer to execute any or all of the steps of the methods disclosed in this application.
The linear AOS array of this invention has the following advantages in comparison to existing console type AOS systems:
1. The preferred PZT transducers are inexpensive and robust.
2. The preferred PZT transducers have a exterior surface that can be cleaned, is tough, and is unaffected by condensation and mass-loading (i.e., may be cleaned like the rest of the interior).
3. Calibration is simplified since only range is used for classification.
4. System testing is simple, since there is no need to test many occupant scenarios, the classification being based on simple H-zone presence/absence criteria and the location of the seatback with respect to the person""s head.
5. A simpler processor with less memory can be used to evaluate the signals.
6. Sensor self-test (which optionally may be included) is more robust, since all sensors are pointed down and will by default hit a flat surface (vehicle seat or floor) in the absence of an occupant, which will return an echo, as compared to angled sensors that might not receive an echo during self-test routines due to non-perpendicular surfaces, such as a seat surface at an angle with respect to the sensor direction.
7. The AOS installation is simplified, as no center console modifications are needed. In a retrofit case, for example, the installation comprises simply cutting out a slot in the headliner, flush mounting the integral AOS/transducer array unit by fasteners, adhesives, or other fastening means, and connecting wiring to power source and airbag deployment system.
8. Installation is further simplified since tolerances on angles and displacements can be relaxed (again, only range is computed, which is amplitude independent, and robust to alignment variation). The preferred use of two mirror-image AOS arrays units, one for passenger seat coverage and one for driver seat coverage, would maintain a symmetrical appearance of the vehicle interior.
9. Faster AOS occupancy classification update rate is possible due to simplified processing. The following example case shows typical AOS update rate time ranges with the AOS transducer array of the invention: Given about a 1 meter distance between the sensor and the seat surface, the US echo signal is acquired in approximately 6 ms. The signal is processed within about 4 ms., and the update rate, per sensor, is approximately 10 ms. In a system with 6 sensors, for example, a update rate of 60 ms or less is achievable over the whole zone, without complex processing circuitry or algorithms.
Still faster speeds are possible with the addition of a dynamic-mode switchover in which the AOS system includes sensors (such as a low-G sensor, pre-crash braking sensor, etc.) to determine the existence of a crash-imminent state (i.e., a high probability of the imminent occurrence of a collision or other high-deceleration event). During the existence of a crash-imminent state, the AOS electronics only pings a single ultrasound transducer (or sub-set of the such sensors) which define a front keep-out-zone (KOZ), e.g., the forward sensor(s) can be aimed ahead of the defined H-zone, and be used to define a KOZ. The use of a single sensor or transducer (or a subset) permits a faster AOS update rate during a crash imminent state.
In addition, forward occupant movement motion tracking (e.g., for example into the KOZ) is simple due to the linear arrangement and centerline parallel location of the sensors. The time history of range data can be used by the AOS to determine occupant motion (both motion history and instantaneous velocity), and predict occupant position over future time-increments, which predictions optionally may then be used for ADS control.
10. Ultrasonic interference from entertainment system speakers is minimal, since all sensors point vertically down into the cabin, and speakers are typically positioned on the doors and walls, pointing into the cabin horizontally. There are no rear-view mirror interference issues, as well as no sunvisor interference issues, since the typical H-zone boundary starts some distance rearward of the sunvisor and rear-view mirror.
11. The overhead linear AOS design concept of the invention is applicable to vehicles with a sunroof, as the sunroof can be fit between both driver and passenger units.
12. The unit would be cheaper than current designs, mainly because a less powerful processor is needed, less memory is needed, no grill is needed, no bezel is needed, but only a single-piece sensor mounting piece that holds the sensors and a single circuit board. Cost savings can also be realized due to the elimination of a Faraday cage for the sensors. The range feature is amplitude independent, and works well under low SNR (Signal-to-Noise Ratio) conditions; sensor deterioration over time would not affect performance.
13. The linear array AOS system optionally functions as an intrusion/anti-theft system, on both driver and passenger sides, the AOS system including an algorithm to use the US range data to determine an intrusion (presence of an occupant when system is armed in an anti-theft mode) into the vehicle. In response the array of the present invention outputs a signal to an anti-theft device, such as an audible alarm. The linear AOS array can be extended to cover the back seats with conventional modifications. Additional sensors (such as IR, mass sensor, etc.), even where not needed for classification, may optionally be included in the AOS for temperature control, for example.